This invention relates generally to aerial lifts and more particularly to an aerial lift which has a horizontally movable pivot point.
In building construction and maintenance, mining, storage/retrieval operations and many other fields, it is often necessary to provide aerial lifts for moving equipment and/or personnel. These lifts have generally been of two types; i.e., cranes and adjustable scaffolds. Conventional cranes are capable of lifting very large loads to relatively great heights. These cranes are usually vehicular to facilitate movement to the job site. When actual lifting is performed, however, the base of the crane, or the vehicle on which it is mounted, is ordinarily fixed in position by stabilizing pads. Since most cranes consist essentially of pivotable booms, this results in the pivot point being fixed. Thus, unless the boom is extensible, as the position of the boom is varied, the load end of the boom moves in an arc. If a load is suspended from the boom, this action will cause the load to swing toward the boom pivot end and, more importantly, toward the boom operator, thus increasing the safety hazards inherent in such operations. If the crane is being utilized to elevate workmen and/or equipment along a vertical plane, the load end necessarily moves increasingly further from said plane as the boom angle increases.
These disadvantages are often overcome by providing extensible, ordinarily telescoping, boom sections. These boom sections are ordinarily extended by power cylinders which extend to force the telescoping boom section outward. Thus, as the boom angle is increased, the power cylinder is extended by the operator thus increasing the length of the boom. This insures that the boom load end moves in a substantially vertical line. This extensible power cylinder dramatically increases the cost of such units. Also, to insure proper, safe operation, a highly skilled operator is required. The operator must pay close attention to retain the load in the original vertical plane. Even with a highly skilled, attentive operator this is often a very difficult procedure since the operator's line of sight is often inadequate to provide accurate adjustments. Due to the line-of-sight problem a second operator is often placed in closer proximity to the load end. This not only increases the cost of operating the crane, but also increases safety hazards since the possibility of misunderstanding between operators is ever present. While boom mechanism may be automated to retain the load in the same vertical plane, such automation systems are quite expensive.
Adjustable scaffolds are often utilized to move loads along a vertical plane. Scissors-type scaffolds, such as that described in my co-pending application, Ser. No. 738,599 filed Nov. 3, 1976, have been found to be advantageous. However, since such apparatuses do not provide a capability of lateral movement, they are limited in their scope of operation. If a simple, nonextensible crane were mounted on an adjustable scaffold, the reaching coverage of the apparatus is still limited, as discussed further hereinbelow and illustrated in the drawings.
Accordingly, one object of the present invention is the provision of a crane which need not have an extensible power cylinder for lengthening the boom but which can move a load in a substantially vertical plane. Another object is provision of a crane which can be easily automated. Yet another object is provision of an aerial lift which is simpler than present lifts but which has greater versatility and lifting range. These and other objects, features, and advantages of the present invention will be apparent from the following description, appended claims, and annexed drawings.